There are many types of topical antiperspirant products that are commercially available or otherwise known in the antiperspirant art. Most of these products are formulated as aerosol or pump sprays, roll-on liquids, creams, emulsions, gels, gel-solids, or other solid stick formulations, and comprise an astringent material, e.g. zirconium or aluminum salts or combinations thereof, incorporated into a suitable carrier. These products are designed to provide effective perspiration and odor control while also being cosmetically acceptable during and after application on to the axillary area or other areas of the skin.
Within this product group, solid antiperspirant sticks have become especially popular among consumers. These antiperspirant sticks comprise a solid matrix within which the antiperspirant active material is contained. The active can be solubilized in a liquid carrier comprising water, glycols and/or other alcohols, or maintained within a solid matrix as dispersed solids in an anhydrous system. The solid sticks which contain dissolved active often provide some low residue performance, but tend to be wet or sticky during and immediately after application to the skin, and more importantly, are often not as effective in providing antiperspirant and deodorant performance as solid sticks containing dispersed particulate active. Although the antiperspirant sticks which contain particulate actives are more effective, they also tend to leave a higher visible residue on the skin.
There have been many attempts at producing anhydrous antiperspirant sticks which contain dispersed particulate antiperspirant active, and which also provide improved efficacy and low residue performance during and after application to the skin, or which otherwise provide product clarity prior to (as a packaged product) or after such application (as a clear or low-residue film on the skin).
One such attempt involves the combination of particulate antiperspirant active, gellants and liquid carrier in a gel stick, wherein all such components in the combination have matching refractive indices. Refractive index matching allows for more passage of light through the gel stick with less scattering of the light, thus resulting in products which appear more clear or translucent as a packaged composition or when initially applied topically to the skin. These gel sticks, however, are expensive to make due to the cost of using raw materials having only select matching refractive indices. These compositions are also very difficult to formulate given that refractive index matching for a three component system (particulate active, solvent and gellant) is extremely difficult, and greatly limits the materials that can be used to prepare such a formulation.
Another attempt at making low residue antiperspirant sticks involves the use of gellants such as dibenzylidene alditols. These gellants, however, like many other gellants known in the art, are not acid stable and therefore tend to interact with the antiperspirant active due to the acidic nature of the active. This interaction can result in reduced efficacy of the active, poor gel formation; and lower gel stability over extended periods during shipping or storage. This interaction may also cause processing difficulties at the temperatures and holding times often used during the formulation and manufacturing process. These gellants are also commonly used in combination with glycol carriers or other solvents which tend to be wet and sticky and irritating to the skin.
Yet another attempt at making low residue antiperspirant sticks involves the use of residue masking agents such as non-volatile paraffinic hydrocarbon fluids, phenyl trimethicone, low melting point waxes and combinations thereof. These agents are used in combination with stearyl alcohol or other high residue waxes commonly used in solid antiperspirant sticks. These agents help reduce visible residue during and immediately after application of the solid stick to the skin, but also tend to be associated with an oily or sticky skin feeling during application. Moreover, although the visible residue is reduced in such compositions, there remains a visible residue on the skin when used in combination with high residue waxes such as stearyl alcohol, and this reduced residue is still more visible or apparent than the topical residue left by antiperspirant sticks which contain solubilized antiperspirant active.
Other attempts at improving low residue performance from an antiperspirant composition has focused on the use of anhydrous antiperspirant creams. These creams can be applied to the skin by conventional means, or by a cream applicator device, and results in very low residue during and immediately after application to the skin. These compositions comprise particulate active dispersed throughout an anhydrous carrier, and either contained within a solid-like matrix or thickened with an inorganic or polymeric gellant or thickening agent. Many consumers, however, still prefer the convenience of using a solid antiperspirant stick, even if the solid stick tends to leave a higher visible residue on the skin.
A recent method of making low residue antiperspirant sticks is described in U.S. Pat. No. 5,429,816, issued to Hofrichter et al. on Jul. 4, 1995, which description is hereby incorporated by reference herein. The antiperspirant sticks provide low visible residue during and immediately after application to the skin, and are physically and chemically stable over extended periods of time. The improved antiperspirant sticks comprise a dual gellant system having a primary gellant such as 12-hydroxystearic acid or esters or amides thereof and a secondary gellant such as n-acyl amino acid derivatives. Formation of such an antiperspirant stick with such a dual gellant system has been characterized as a "gel-solid" antiperspirant stick. .An antiperspirant gel-solid, such as that described by Hofrichter et. al., is an antiperspirant stick having a three-dimensional, non-polymeric, gel network in which solvent is contained or trapped. These gel-solids are typically formed by solubilizing the gellant in the solvent at temperatures above the melt point of the gellant and at temperatures at which the melted gellant is soluble in the solvent, and then cooling the composition to form the desired gel-solid composition. The low residue gel-solids described by Hofrichter et al. are remarkably stable, both physically and chemically, and will maintain the desired product hardness over an extended period of time. The gel-solids described by Hofrichter et al., however, are limited to select dual gellant systems and do not include or otherwise describe any method of making a low-residue antiperspirant gel-solid stick containing any other gellant or gellant system.
It has now been found that other low-residue gel-solids can be formulated without reliance upon the select combination of gellants described by Hofrichter et al. The new low-residue gel-solids are anhydrous systems which comprise from about 0.5% to about 60% by weight of particulate antiperspirant active; from about 1% to about 15% by weight of a solid non-polymeric gellant that is substantially free of dibenzylidene alditol, or n-acyl amino acid derivatives; from about 10% to about 80% by weight of an anhydrous liquid carrier for the solid non-polymeric gellant having an average solubility parameter ((cal/cm.sup.3).sup.0.5) of from about 3 about 13 and wherein the composition has a visible residue index of from about 11 to about 30 L-value, a product hardness of from about 500 gram-force to about 5,000 gram-force, a ratio of an elastic modulus (G') to a viscous modulus (G") of from about 0.1 to about 100. The composition should be substantially free of inorganic or polymeric thickening or gelling agents, and does not require refractive index matching of the particulate antiperspirant active, solid non-polymeric gellant, and anhydrous liquid carrier to obtain low residue performance. The compositions preferably comprise gellant crystalline particles having an average particle size of less than about 1 .mu.m, and/or an elongated particle morphology defined by an aspect ratio of greater than about 2.
It is therefore an object of the present invention to provide an anhydrous antiperspirant gel-solid stick containing particulate antiperspirant active which provides improved low residue performance and improved antiperspirant efficacy, and further to provide such a composition without reliance upon specific gellants such as dibenzylidene alditols or dual gellant systems containing n-acyl amino acid derivatives. It is a further object of the present invention to provide such a composition without reliance upon refractive index matching of component materials, or the use of solubilized antiperspirant active, to obtain product clarity or low residue performance. It is yet another object of the present invention to provide such a composition that is physically and chemically stable over extended periods of time, and further to provide for such stability in an anhydrous system without reliance upon the use of polymeric or inorganic thickening or gelling agents.